Natural immunity against toxins 333 



their blood, often with very great rapidity. Quite young alligatonj 

 (weighing about 500 grammes) are capable of producing antitoxin, 

 though somewhat slowly. A month after the first injection of the 

 tetanus toxin their blood is incapable of causing tetanus in mice, but 

 is not yet antitoxic. A month later, however, it never fails to prevent 

 an attack of tetanus when mixed with fatal doses of the toxin and 

 injected into mice. 



Older alligators develop antitoxic power much more rapidly, and 

 on several occasions we have found, to our great astonishment, that, 

 as early as 24 hours after injection of the toxin, their blood was 

 distinctly antitetanic. The blood of the same alligators, tested before 

 the injection of the toxin, like the blood of normal alligators 

 generally, exhibited no antitoxic property. 



In several experiments we took the rectal temperature of our 

 animals and were never able to observe the slightest rise correspond- 

 ing to the temperature of the water in which the alligators lived. 



It cannot be doubted then, that, in spite of the facility with which [350] 

 these reptiles produce tetanus antitoxin, their immunity does not 

 depend on this antitoxic property. Thus, young alligators which 

 have resisted a single dose of toxin sufficient to kill 6000 mice must 

 owe their immunity to some other cause than the antitoxic power of 

 the body fluids, for their blood does not begin to exhibit this 

 property until two months after injection. 



These same reptiles are also very refractory against cholera toxin, 

 even in large doses ; they react to the injection by the development 

 of the corresponding antitoxin. On the other hand they are very 

 susceptible to diphtheria toxin, small quantities of which are quite 

 sufficient to bring about a fatal intoxication. 



Snakes, like other reptiles, are refractory against tetanus toxin. 

 In the study of their natural immunity, however, we are confronted 

 by the difficulty that their blood is naturally toxic for laboratory 

 animals. This toxin, analogous to the ichthyotoxin of eel's serum, has 

 been compared with snake venom against which the snakes them- 

 selves enjoy a very marked immunity. 



Not venomous snakes only exhibit immunity against their own 

 poison. Long ago Fontana^ observed that non- venomous snakes 

 resist the bite of the viper and even subcutaneous inoculation of 

 its venom. Phisalix and Bertrand^ confirmed these observations 



1 " Traite sur le venin de la vip^re," Florence, 1781. 



» Arch, dephysiol norm, et path.^ Paris, Ann6e xxvi, 1894, p. 423. 



